This invention relates generally to ultraviolet light treatment of fluids and more particularly, to optical sensing and control of ultraviolet light intensity levels in an ultraviolet light fluid treatment process with photodiode detectors.
Ultraviolet (UV) light may be used to sterilize water and other fluids. The ultraviolet light disrupts the DNA of microorganisms in the fluid, which prevents reproduction and thus kills the microorganisms. Regulation of UV light intensity is important in the UV light sterilization process because a minimum level of ultraviolet light intensity is typically required. Also, excessive levels of UV light intensity can result in high maintenance and an associated higher operation cost.
Photodiodes are sometimes used to detect and regulate UV light intensity in such sterilization processes. The UV light spectrum includes wavelengths from 10 to 400 nanometers (nm). However, typical photodiodes used to measure UV light in the known UV light sterilization processes are usually broad range wavelength detectors. For example, silicon detectors are used which are sensitive to light wavelengths ranging from 200 to 1100 nm. Gallium arsenide phosphide and gallium phosphide detectors, which are sensitive to light wavelengths ranging from 200 to 650 nm, are also used. These devices are inherently sensitive to visible and infrared light waves in addition to the UV spectrum. When only UV light detection is desired and outside light sources such as visible light are also present, erroneous signals may result.
Therefore, filters are needed to block out wavelengths longer than 400 nm to eliminate erroneous signals triggered by other light sources. However, filters are prone to degradation which can lead to permitting light out side the UV spectrum into the detector, which results in false and inaccurate readings. Additionally, filter degradation results in costly maintenance and/or equipment downtime.
It would be desirable to provide an ultraviolet light sterilization process incorporating a UV detector that is not sensitive to light outside the UV spectrum to eliminate erroneous signals caused by ambient light sources. It would further be desirable to provide an ultraviolet light sterilization process that does not depend upon light filters thereby lowering g maintenance costs and equipment downtime due to filter repair or replacement.
In an exemplary embodiment, an ultra violet light sterilizing apparatus utilizing a photodiode sensor includes a silicon carbide (SiC) photodiode, a gallium nitride (GaN) photodiode, or an aluminum gallium nitride (AlGaN) photodiode. The ultraviolet light fluid sterilization apparatus includes a fluid chamber, at least one ultraviolet light source configured to emit ultraviolet light into the fluid chamber, and at least one ultraviolet light sensor that includes a photodiode.
Each UV light sensor includes a sealed outer housing having an optically transparent window. A silicon carbide photodiode, a gallium nitride photodiode, or an aluminum gallium nitride photodiode is located inside the housing adjacent the transparent window. The housing also includes at least one sealable outlet to permit electrical wire connections to pass into the housing. The optically transparent window may be fabricated from sapphire or quartz.
The UV light fluid sterilization a pparatus further includes a controller for sampling the signal from each ultraviolet light sensor. The controller compares the sampled signals to a desired UV light intensity and outputs a control signal to each ultraviolet light source to adjust the intensity of the ultraviolet light emitted from each ultraviolet light source.
In operation, fluid flows into the chamber of the ultraviolet light sterilization apparatus. The fluid is then irradiated with UV light from the ultraviolet light source. The UV light sensor measures the intensity of the UV light inside the chamber of the apparatus and the controller samples the signal generated by the sensor. Particularly, the photodiode senses the intensity of the UV light inside the chamber, the signal amplification unit amplifies the signal, and the controller samples the signal generated by the sensor. The controller ascertains any difference between the sensed UV intensity and a predetermined desired UV intensity. The controller then adjusts the intensity of the ultraviolet light source to correspond to the predetermined level of UV intensity.
The above described ultraviolet light fluid sterilization apparatus utilizes a UV detector that is not sensitive to light outside the UV spectrum and thus eliminates erroneous signals caused by ambient light sources. Particularly, the UV sensor has good UV sensitivity in the 200 to 300 nm band and is insensitive to infrared radiation above 400 nm. Also because the UV sensor is not sensitive to light having wavelengths greater than 400 nm, light filters are not required to filter ambient light.